HEASoft, the FTOOLS and XANADU
software package maintained at the HEASARC, is recommended for the analysis of
NuSTAR data. The current version (6.16) of HEASoft which
was released on July 2nd, 2014, contains a NuSTAR subpackage of tasks -
NuSTARDAS - which, together with the existing FTOOLS and XANADU tasks, will
enable users to do a complete analysis of NuSTAR datasets, with perhaps a few
For more detailed information, see the
NuSTAR data analysis software users guide, v1.7.1 (1.4 MB PDF file)
NuSTAR data analysis quickstart guide, v1.1 (2.3 MB PDF file).
NuSTAR Calibration and Background-Subtraction Information
Documentation with information about the calibration of the NuSTAR
observatory will be available shortly (Madsen et al. 2014, in preparation).
A detailed examination of the components of the NuSTAR background can be
found in the appendix of Wik et al.
(2014, ApJ, 792, 48).
NuSTAR Analysis Caveats
- We do not recommend using XSELECT to manually generate high level
products (images/spectra/light-curves) from the event files, as there are
NuSTAR-specific FTOOLS that are required to accurately reproduce the livetime
of the instrument. If XSELECT is used to manually filter event files, the
'nulivetime' FTOOL *must* be run in order to correct the LIVETIME keyword
(XSELECT overwrites this keyword during the filtering step). However, we
re-iterate that we do not recommend manually filtering data and producing
high-level products in this manner as there is a significant risk of
introducing some errors. Instead, if GTI filtering is required, we recommend
that the users should use XSELECT to generate the GTIs and then use
'nupipeline' and 'nuproducts' with the 'usrgti' keyword to ensure that the
high level products are correct.
- We do not, in general, recommend co-adding data from the two NuSTAR
telescopes for spectroscopic analyses. Simultaneously fitting the data from
the two telescopes by leaving a floating cross-normalization parameter (e.g.
including leading "const" model term in XSPEC) will provide more accurate
results. If the "const" for FPMA is frozen to unity, then the "const" value
for FPMB is typically between 0.95 and 1.05, depending on how far off-axis
the source is in each telescope.
Co-adding the effective areas of the two NuSTAR instruments without first
accounting for the cross-normalization may introduce systematic errors in the
model parameters. However, this should only be significant for analysis of high
signal-to-noise observations when the systematic errors will be large compared
to the statistical errors.
For analysis of low signal-to-noise observations (e.g. to test for
detectability), when the statistical errors will be large compared to
systematic errors, or when the user wishes to combine two observations from
different epochs for the same telescope, we recommend the following two
(1) For HEASoft 6.16 and earlier versions without the patch to cmprmf released
on 2015/01/23, we recommend using
addascaspec to combine the PHA files, background PHA files,
and ARFs, and addrmf
to combine the RMFs.
(2) For HEASoft 6.16 with the patch to cmprmf applied, we recommend using
addspec which will combine the source and background PHA files as
well as the RMFs and ARFs.
Other Known NuSTAR Analysis Issues
These will be addressed in a future release of NuSTARDAS and NuSTAR CALDB.
The NuSTARDAS module that will be updated is indicated in parentheses ():
- NuSTARDAS v1.4.1 (released as part of HEASOFT 6.16) is not compatible
with NuSTAR CALDB version 20131223. In particular, nupipeline will fail
when trying to process data with NuSTARDAS v1.4.1 and version 20131223 of the
NuSTAR caldb. NuSTARDAS v1.4.1 users should either make sure they have
version 20140414 of the NuSTAR CALDB installed locally or that they are using
to access the latest NuSTAR CALDB from the HEASARC.
Previous NuSTAR Analysis Issues Which Have Been Fixed
 means the issue was fixed in NuSTARDAS v1.3.0 (released with HEASOFT
 means that the issue was fixed in CALDB release 20131007.
 means that the issue was fixed in CALDB release 20131223.
 means the issue was fixed in NuSTARDAS v1.3.1 (released with
- An adjustment of the NuSTAR FPM effective areas above 50 keV was needed to correct for the residuals of the W k-edge (69.5 keV) and the Pt k-edge (78.4 keV) in CALDB version 20131007 (and earlier). Analysis of very bright objects may show smooth residual features of order 5 - 15% at energies above 50 keV. This adjustment was included in the NuSTAR CALDB patch 20131223, which was released on January 17, 2014. 
- As of
CALDB version 20131007, the NuSTAR clock correction file for use with the
FTOOL barycorr is available within the standard HEASARC CALDB releases/patches.
It is also available from the
NuSTAR SOC website. 
- Bad/hot pixels were only approximately accounted for in the exposure
maps. There is now an
improved algorithm for inclusion of bad/hot pixels in exposure maps which
requires new CALDB files of instrument cumulative probability maps. (nuexpomap)
- The energy dependence of the vignetting correction to PSF was not
taken account of. The corrections for the dependence of the PSF on energy are
at most 5%. This correction, performed in 6 energy bands (3-4.5, 4.5-6,
6-8, 8-12, 12-20, 20-79 keV), required new CALDB PSF files. (numkarf) 
- There was a processor memory issue handling temporary FITS files in
the extended source case when using a small value of the input parameter
'boxsize'.This was fixed. (numkarf) 
- A correction for energy-dependent PSF losses in lightcurve file
generation required using new CALDB PSF files. (nulccorr) 
- Adjustment of the NuSTAR FPM effective areas by +15% placed NuSTAR
measured fluxes between Swift and XMM measurements based on simultaneous
observations of calibration targets in 2012. 
- The value of the DEADC FITS keyword affected how lightcurves are displayed.
The "DEADC" FITS header keyword in the NuSTAR lightcurve files (produced by
nuproducts/nupipeline) contains the average livetime fraction over the course
of the observation (i.e. the livetime integrated over GTIs divided by the
"real" seconds integrated over the GTIs). Some standard tools for plotting
lightcurves (i.e. the "lcurve" FTOOL) read the DEADC FITS header keyword value
and apply this value to the displayed lightcurve. However, the nulccorr FTOOL
in NuSTARDAS v1.3.0 (and previous versions) applied a deadtime correction to
each individual bin in the lightcurve. Thus using lcurve to display a NuSTAR
lightcurve which has been corrected by nulccorr (as is the default for
nupipeline/nuproducts) resulted in a "double counted" deadtime correction in
the displayed lightcurve, and as a result over-estimated the source flux in
each bin. In the meantime users can work around this by either a) setting the
DEADC keyword values to 1.0 in the the NuSTAR lightcurve file before using
lcurve or b) using the DEADC value to rescale the lightcurve displayed in
lcurve. For example:
% lcurve 1 out5.lc  rescale=0.92
where out5.lc is a lightcurve file generated by nuproducts (with the parameter
correctlc="yes") and 0.92 is the value of the DEADC keyword in out5.lc. 
The pilow/pihigh input parameters in nupipeline/nuproducts define the
energy band over which the lightcurve is produced but as of NuSTARDAS v1.3.0
were not applied to images or spectra. The plan is to update nupipeline and
nuproducts to use the pilow/pihigh keywords for image generation also so that
nuproducts/nupipeline can be used to produce images as well as lightcurves in
the specified energy band. For users with NuSTARDAS v1.3.0 installed
(distributed as part of the heasoft-6.15 release) we recommend using the
extractor" FTOOL or XSELECT
to generate images over a given energy band. 
The PIXBIN and PERC values were missing from the exposure map FITS
header. The PIXBIN and PERC parameters drive the performance of nuexpomap and
should have been included in the FITS header for self-documentation purposes.
As of the date of the 3rd NuSTAR data release on February 5th, 2014, the notes
for specific NuSTAR ObsID's that used to be found on this page
are now captured in several
parameter for those ObsIDs in the
NUMASTER table. Potentially problematical issues are indicated by
the parameter issue_flag in the NUMASTER table having
a value set to 1. The specific nature of the issue affecting the
observation will be indicated in one or more non-blank or non-zero
values of the following parameters in NUMASTER:
In addition, the
parameter in NUMASTER lists observatories for which coordinated observations
were made with the specified NuSTAR observation. The
parameter in NUMASTER contains a brief text synopsis of the major known
issues and unusual features.